This investigation was undertaken to determine the sensitivity of the damping factor in a large space structure (LSS) to small changes in nonstructural mass and structural element stiffness. Revision 3 of the ACOSS 2 model, developed by the Charles Stark Drapes Laboratory, Inc. (CSDL), was used as the model of the LSS. Various combinations of the mirror masses in this large space telescope were varied by up to 10%, selected structural elements were stiffened by increasing their cross-sectional areas by 10 and 50%, and, finally, two structural elements in the middle of the telescope were stiffened to represent the addition of a lumped mass located away from the control system sensors and actuators. A control system of 21 collocated sensors and actuators, positioned at the top and bottom of the telescope, was used in this analysis. The analysis was accomplished using NASTRAN for the finite element analysis, and, after selecting certain vibration modes for further study, the complex conjugate pairs used to determine the damping factors were calculated. The results indicate that the damping factors for the CSDL model are quite sensitive to small perturbations and that it is very difficult to predict the effect that a perturbation to the model will have on the damping factors.

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